1. Technical Field
The present invention relates to a flexible optical waveguide which has the characteristic of following curves and twists, and to a soft flexible optical waveguide which has the characteristic of following curves and twists.
2. Related Art
Heretofore, methods for fabrication of polymer optical waveguides have been proposed, such as: (1) a method of impregnating films with a monomer, selectively exposing a core portion to alter a refractive index, and sticking together the films (the selective polymerization method); (2) a method of coating a core layer and a cladding layer and then using reactive ion etching to form a cladding portion (the RIE method); (3) a method of using an ultraviolet-curable resin in which a photosensitive material has been added into a polymer material, and using a photolithography process for exposure and development (the direct exposure method); (4) a method which utilizes injection molding; (5) a method of coating a core layer and a cladding layer, and then exposing a core portion to alter refractive index of the core portion (the photo bleaching method); and so forth.
However, the selective polarization method of (1) has problems in sticking the films together, costs are high with the methods of (2) and (3) because a photolithography process is used, and the process of (4) has problems with precision of a core diameter that is obtained. Further, the method of (5) has problems with a sufficient refractive index difference between the core portion and the cladding portion not being provided.
Only the methods of (2) and (3) have excellent characteristics in practice, but have problems with cost as mentioned above. Thus, none of the methods of (1) to (5) can be applied to forming polymer optical waveguides on flexible plastic base materials with large areas.
Now, as a method which is completely different from conventional methods for fabricating polymer optical waveguides as described above, the present inventors have invented and filed applications on a method for fabrication of a polymer optical waveguide which utilizes a mold, which is referred to as a micromolding method. According to this method, it is possible to manufacture polymer optical waveguides extremely simply at low cost. In addition, in spite of the simplicity of the method, it is possible to fabricate polymer optical waveguides with low waveguide losses, and it is possible to easily fabricate waveguides with any form of pattern in which it is possible to fabricate a mold. Furthermore, it is possible to fabricate optical waveguides on flexible plastic base materials, which have been difficult to fabricate heretofore.
Meanwhile, with improvements in processing capabilities of computers in recent years, a problem has arisen with the ‘wiring bottleneck’, in that electrical wiring between computers and various other devices limits overall capabilities of systems. Accordingly, optical interconnection (optical wiring) has drawn attention as an effective means for overcoming this wiring bottleneck, because there are no signal delays due to impedance as in electrical wiring and inter-wiring interference does not occur.
In optical wiring, an optical transmission/reception module is a key structural component. An optical transmission/reception module propagates light emitted from a light emission element through an optical waveguide, detects light that has been propagated through the optical waveguide with a light reception element, and thus is a module which performs transmission and reception of optical signals.
At a polymer optical waveguide formed with a polymer material, which serves as an optical waveguide to be used with such an optical transmission/reception module, it is possible, by forming optical wires which are matched with light emission/reception elements in an array, to connect optically between the plural light sensors and core portions of the corresponding polymer optical waveguides all at the same time. Further, it is possible to prepare a 45° micromirror surface simply, with a dicing saw or the like, and thus a compact 90° light path change is possible (i.e., an alteration from a wave-guidance direction to a direction which is orthogonal to a film surface). Thus, because it is possible to alter an optical path that connects with a surface-form light emission/reception element, which is surface-mounted, to be parallel with the mounting surface, a low cost light transmission/reception module can be realized.
Further, usement of optical wiring at movable portions, such as hinges of notebook-type computers and folding-type portable telephones, has been considered. A flexible type of polymer optical waveguide which features characteristics of following along with twists and curves, as does a flexible printed base material which is used for electrical wiring, has been investigated. For this flexible-type polymer optical waveguide (flexible optical waveguide), a core in which light is propagated and a cladding which is provided around the core are both fabricated with a material with a low flexural modulus, such as a gel material or the like, and feature flexibility as a whole.
However, in a case in which overall high flexibility is provided in a polymer optical waveguide, deformations are likely to be caused by external forces in pickup, bonding and the like of a mounting process. Consequently, separation between cores when optically connecting at light emission and reception elements is not preserved, positional relationships between cores and alignment marks are not preserved, and mounting with sufficient accuracy is difficult. Furthermore, in a process of preparing a 45° micromirror surface with a dicing saw, because there is flexibility, it is difficult to process a flat surface with high accuracy.